Some deer are protected from deadly disease by genetics

In the summer of 2022, reports of dead deer were on the rise in rural properties due to a viral illness. According to the Urbana Park District, Epizootic Hemorrhagic Disease (EHD) occurs in white-tailed deer populations around the state of Illinois every few years. Once deer are infected, they die within days. Now, University of Illinois scientists have identified gene variants in deer that are associated with susceptibility to the virus.

“This is the first time this gene has been sequenced completely in white-tailed deer. This is important because without the sequences, there’s no starting point to do any kind of research,” said study co-author Alfred Roca, a professor in the Department of Animal Sciences. 

The team sequenced the gene for Toll-Like Receptor 3 (TLR3), a protein that spans membranes in immune cells and helps recognize double-stranded RNA (dsRNA) viruses. When a dsRNA virus enters the cell, TLR3 activates immune defenses, triggering inflammation and priming the rest of the immune system.

The study found dozens of variable sites in the DNA, known as single-nucleotide polymorphisms (SNPs). Two of the SNPs were significantly more common in uninfected deer.

“Because we found mutations in TLR3 more frequently in EHD-negative animals, we think deer with these mutations are less susceptible to EHD,” said co-author Yasuko Ishida.

Many white-tailed deer are exposed to EHD in their lifetimes, but only some will die from the disease. Outbreaks occur every three to five years, when environmental conditions favor the life cycle of midges that carry the virus. 

Midges spend their larval stages in mud under the ponds and puddles that deer drink from during drought conditions. In the late summer, the water sources dry up, and the adult flies emerge to bite and infect deer. This cycle does not occur annually, as it is interrupted by rain or a cold snap.

There are no options available to wildlife managers to prevent outbreaks in natural habitats. The researchers say it’s still helpful to understand the genetic underpinnings of the disease. This study will also help to inform the public on what the disease looks like and the severity of an outbreak. 

The disease is an increasing threat to the state’s northern regions. Another recent study shows the disease has been slowly but steadily moving northward, either due to climate change or greater reporting.

Study lead author Jacob Wessels completed the research as part of his master’s degree and now serves as a conservation police officer with the Illinois Department of Natural Resources.

“It’s very complicated to respond to an outbreak of EHD because there are often large numbers of deer found dead near water,” said Wessels. “People don’t know what to do when that happens, but we encourage the public to report potential EHD outbreaks to their local IDNR wildlife biologist for the surveillance and future study of the disease.”

The research is published in the journal Genes.

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By Katherine Bucko, Earth.com Staff Writer

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